Tao Gui

Experimental study of PAM-4, CAP-16, and DMT for 100 Gb/s short reach optical transmission systems.

Advanced modulation formats combined with digital signal processing and direct detection is a promising way to realize high capacity, low cost and power efficient short reach optical transmission system. In this paper, we present a detailed investigation on the performance of three advanced modulation formats for 100 Gb/s short reach transmission system. They are PAM-4, CAP-16 and DMT. The detailed digital signal processing required for each modulation format is presented. Comprehensive simulations are carried out to evaluate the performance of each modulation format in terms of received optical power, transmitter bandwidth, relative intensity noise and thermal noise. The performance of each modulation format is also experimentally studied. To the best of our knowledge, we report the first demonstration of a 112 Gb/s transmission over 10km of SSMF employing single band CAP-16 with EML. Finally, a comparison of computational complexity of DSP for the three formats is presented.

Nonlinear Frequency Division Multiplexed Transmissions Based on NFT

We experimentally demonstrate the successful modulation and error-free detection of three eigenvalue nonlinear frequency division multiplexed (NFDM) signals over 1800 km based on the recently developed nonlinear Fourier transform theoretical framework with digital coherent receivers. The three eigenvalues are located on the upper-half complex plane and are modulated by independent ON-OFF keying signals, thus forming 3-bit NFDM symbols for nonlinear fiber transmissions.

Efficient MMSE-SQRD-Based MIMO Decoder for SEFDM-Based 2.4-Gb/s-Spectrum-Compressed WDM VLC System

A spectrally efficient frequency division multiplexing (SEFDM) modulation has been proposed to improve system spectral efficiency, particularly for bandwidth-limited visible-light communication (VLC) systems. It employs non-orthogonal subcarriers to achieve bandwidth savings at the expense of serious intercarrier interference (ICI); thus, complicated detectors are required at the receiver to extract signals from the ICI. In this paper, we carry out an analysis of SEFDM modulation and establish a quasi-multiple-input multiple-output (MIMO) model for SEFDM-based systems. Based on this quasi-MIMO system model, for the first time, we propose to use an MMSE-sorted QR decomposition (MMSE-SQRD)-algorithm-based MIMO decoder to efficiently eliminate the ICI in a high-speed SEFDM-based wavelength-division multiplexing (WDM) VLC system. Using the MMSE-SQRD decoder, the WDM VLC system at an aggregate data rate of 2.4 Gb/s is experimentally demonstrated over a 2-m indoor free-space transmission, and up to 20% of bandwidth savings is achieved compared with that of the orthogonal frequency-division multiplexing (OFDM). The results clearly validate the effectiveness of the proposed MMSE-SQRD detector for SEFDM-based spectrum-compressed VLC system.

High-order modulation on a single discrete eigenvalue for optical communications based on nonlinear Fourier transform

In this paper, we experimentally investigate high-order modulation over a single discrete eigenvalue under the nonlinear Fourier transform (NFT) framework and exploit all degrees of freedom for encoding information. For a fixed eigenvalue, we compare different 4 bit/symbol modulation formats on the spectral amplitude and show that a 2-ring 16-APSK constellation achieves optimal performance. We then study joint spectral phase, spectral magnitude and eigenvalue modulation and found that while modulation on the real part of the eigenvalue induces pulse timing drift and leads to neighboring pulse interactions and nonlinear inter-symbol interference (ISI), it is more bandwidth efficient than modulation on the imaginary part of the eigenvalue in practical settings. We propose a spectral amplitude scaling method to mitigate such nonlinear ISI and demonstrate a record 4 GBaud 16-APSK on the spectral amplitude plus 2-bit eigenvalue modulation (total 6 bit/symbol at 24 Gb/s) transmission over 1000 km.

Single Channel 50 Gbit/s Transmission Over 40 km SSMF Without Optical Amplification and In-Line Dispersion Compensation Using a Single-End PD-Based PDM-SSB-DMT System

We experimentally demonstrate a single-end photodetector (PD) based polarization-division-multiplexing (PDM) system, in which the single-sideband orthogonal frequency-division multiplexing (SSB-OFDM) and discrete multitone (DMT) signals are modulated on two orthogonal polarizations respectively. Based on the frequency interleave design for dual-polarization, the spectral efficiency and chromatic dispersion tolerance can be optimized. We derive the theoretical model for the PDM-SSB-DMT system and detail the digital signal processing for demultiplexing at the receiver. We also successfully transmit a 50 Gb/s PDM-SSB-DMT signal with 14 GHz bandwidth over 40 km of uncompensated and unamplified standard single mode fiber (SSMF) with only 1.1 dB power penalty for a bit error rate of 3.8 × 10–3 relative to back-to-back transmissions.

Phase modulation on nonlinear discrete spectrum for Nonlinear Frequency Division Multiplexed transmissions

We investigated phase modulation on nonlinear discrete spectrum for Nonlinear Frequency Division Multiplexed transmissions and characterized the effects of filtering, launched power fluctuations and laser phase noise on system performance.

Noise Correlation between Eigenvalues in Nonlinear Frequency Division Multiplexing

The noise effects on signals with multiple eigenvalues is studied numerically. Correlations between the noise of the eigenvalues are discovered for the first time, which allows a more compact pack of signal points.

Advanced modulation formats for 100Gb/s/lambda short reach applications

Advanced modulation formats combined with digital signal processing and direct detection is a promising way to realize high capacity, low cost and power efficient short reach optical transmission system. In this paper, we have studied and compared several advanced modulation formats in terms of performance and implementation complexity for 100Gb/s/lambda short reach transmission systems.

Coherent-detection-assisted BOTDA system without averaging using single-sideband modulated local oscillator signal

A novel setup for coherent-detection-assisted Brillouin optical time domain analysis (BOTDA) is proposed and demonstrated. Performance enhancement is enabled by a power-controllable local oscillator (LO) generated using single-side-band (SSB) modulation. Through employing a commercial coherent receiver and polarization diversity scheme, the Brillouin gain traces carried on a stable intermediate frequency (IF) are obtained in real time without any averaging and processed by digital signal processing (DSP) without the need of ultra-narrow optical band pass filter. A spatial resolution of 4 m and frequency uncertainty of 1.473 MHz are achieved over 40 km sensing range using a single scan.

PDM-SSB-OFDM transmission over 80km SSMF based on a single photodetector at C-band

We experimentally demonstrated an 80-Gb/s PDM-SSB-OFDM transmission over 80km SSMF at C-band using a single photodetector. The two SSB-OFDM signals are placed with the different center frequency to share the guard band. The required OSNRs at 7% overhead HD-FEC threshold are 28.5dB and 29dB for BTB and 80km transmission respectively.